With the reduction of the size of selective call receivers and the need for portableness and convenience, selective call receivers primarily depend upon battery power supplied by limited energy content batteries. Thus, users desire power conserving methods in the selective call receivers which improve battery life. One of the primary current draining circuits in a selective call receiver is the receiver circuitry. The receiver circuitry must necessarily be energized to allow the selective call receiver to receive radio signals intended for reception by the selective call receiver, however, the receiver circuitry can be de-energized during other operations of the selective call receiver.
An example of a conventional power conserving method involves determining whether the carrier frequency indicates transmissions intended for the radio receiver are being received. It can be quickly determined whether a carrier frequency is received, but a radio system may broadcast numerous types of information on the carrier frequency, some of which are not intended for the selective call receiver which may cause an unknowing receiver to expend battery power unnecessarily.
Selective call receivers can improve battery life by having the receiver circuitry energized only during portions of the preamble of the signalling protocol received and only during the address portions of selective call messages received to determine if a message is addressed to the selective call receiver. But typical battery saving methods require that the receiver circuitry be energized during the reception of a sufficient portion of each address received to perform address correlation to determine quickly whether the address is that of the selective call receiver or not. In addition, typical battery saving methods require that the selective call receiver know when addresses are received within the signalling protocol. For example, conventional battery saving methods can take advantage of the frame assignments and the occurrences of addresses at predetermined positions within the Post Office Code Standardization Advisory Group (POCSAG) signalling protocol. Also, before detection of its address, the selective call receiver must detect the synchronization codeword which enables the selective call receiver to achieve word synchronization.
Thus, what is needed is a battery saving method which would conserve power by energizing the receiver circuitry for periods shorter than conventional detection periods for preamble detection, address correlation and synchronization codeword detection.